The present invention relates to the sealing or encapsulating of cables within a conduit, for example, sealing electrical cables within a duct or conduit provided in the wall of an underground vault. More particularly, the invention is directed to a novel plug assembly and method for encircling the cables and encapsulating them within a vault wall conduit.
Equipment such as electrical power transformers are often installed underground within concrete vaults. The vaults provide an enclosure or housing for protecting the transformers from the elements, and it is necessary to interconnect the transformer with equipment above ground or with transformers contained within other remote underground vaults. Typically, vaults are designed with apertures in their walls for passing therethrough electrical conductors sheathed in dielectrics, such as plastic cables which provide electrical insulation. The cables extend through a suitable conduit provided in the vault wall, and it is necessary to seal the cables within that conduit to prevent water or gas intrusion into the transformer-containing vault.
In addition, transformers to be interconnected may be situated in vaults which are at different elevations. The cables which join the transformers are housed in a conduit which extends from one vault wall to another, but these conduits can become cracked or split due to ground movement or pressure, thereby permitting ingress of water into the conduit. If a break in the conduit occurs near its upper end, it is readily apparent that substantial hydrostatic pressures will be presented to a seal in the lower vault.
There have been many proposals for sealing cables within a conduit at the juncture where the cable passes through the vault wall. These devices, known as "plug assemblies," generally include some type of expandable element for mounting over the cable which will expand to grip the cable directly and also be forced against the internal wall of the conduit to provide sealing. However, there are specific problems concerning providing an adequate seal, not the least of which is that a conduit in the vault wall may be "out-of-round," a condition which occurs when concrete is poured around the conduit during construction resulting in the conduit becoming warped or distorted. Thus, it has been difficult to provide a plug assembly which will expand in a manner to compensate for the asymmetry of the conduit. In addition, the plastic cables which provide a dielectric sheath for the electrical lines may contract or expand, due to various conditions, which tend to break the seal between the plug assembly and the cable. The cables may also "whip," and move back and forth, a condition particularly prevalent in high voltage cable (600 volts and above). In addition, so-called "concentric neutrals," i.e., ground wires, may be spirally woven over the cables which present open areas between the plug assembly and the cables thereby providing a passage for water or gas intrusion.
Moreover, conventional plug assemblies tend to apply concentrated pressure points on the cables which cause the plastic material of the cables to "cold-flow," resulting in uneven electrical insulation around the electrical lines. This can become a significant problem when it is recognized that multiple cables may be disposed through a plug assembly, and if sufficient electrical stresses are created, due to improper insulation because of the "cold-flow" situation mentioned above, electrical shorts can occur.
With the above problems in mind, it is a general object of the present invention to provide a plug assembly for encircling a cable or cables for encapsulation within a vault-wall conduit for engaging the cables with substantially equal radial pressure distribution to avoid concentrated forces or pressure points on the cables which cause the insulation to "cold-flow."
In addition, it is a another object of the present invention to provide a plug assembly which will ensure that if the cables are provided with concentric neutrals, adequate sealing will be provided; moreover, it is an object to provide a plug assembly which will maintain a seal when the cables contract or distort or move longitudinally ("whip") within the plug assembly.
To the above ends, the plug assembly of the present invention includes dual compression members, such as a first ring member formed of flexible or resilient material having an inner wall comformable to a circumferential portion of a cable's outer surface, and a second ring member, disposed adjacent the first ring member, also formed of resilient material which has an inner wall conformable to a circumferential portion of the cable's outer surface. Disposed between the first and second ring members is a substantially rigid spacer means which defines a sealant-receiving channel between the ring members. A compression means associated with the plug assembly is operable for deforming the first and second ring members axially and radially thereby to deform the channel so that at least some sealant material received therein is directed or "squeezed" into the region between the inner walls of the first and second ring members and corresponding portions of the cable's outer surface. The net result is a substantially uniform cushion/sealant presented between the ring members and the cable. Concerning the sealant material, it is contemplated that a suitable silicone compound known as "RTV" (room temperature vulcanizing silicone) is used. The sealant material may be dispensed by means of a caulking gun or the like within the channel, prior to the plug assembly being assembled around a cable or cables.
Another object of the present invention is to provide a plug assembly in which the compression means includes rigid members mounted on the external sides of each ring member, and wherein a biasing means interconnects the rigid members, ring members and spacer means. The biasing means may be manipulated to shift the rigid members toward one another to compress the first and second ring members against the spacer means so that the channel decreases in width, thereby directing sealant material therefrom into the region between the inner walls of the first and second ring members and corresponding outer wall portions of a cable.
Still another object of the present invention is to provide a plug assembly, as set forth above, in which the spacer means includes an arcuate surface facing internally toward a cable. Thus, when the channel is filled with sealant material, the arcuate surface, upon compression of the compression means, ensures that a relatively uniform flow of sealant material to the region between the inner walls of the ring members and outer surfaces of a cable will result, ensuring substantially equal radial pressure distribution.
These and additional objects and advantages of the present invention will be more readily understood after a viewing of the drawings and the detailed description of the preferred embodiment.